1. Field of the Invention
The invention relates generally to offshore structures to facilitate oil and gas production. More particularly, the invention relates to buoyant towers releasably coupled to the sea floor and configured to store and offload produced hydrocarbons.
2. Background of the Technology
Offshore structures are used to store and offload hydrocarbons (e.g., oil and gas) produced by subsea wells. Usually, the type of offshore structure employed will depend on the depth of water at the well location. For instance, in water depths less than about 300 feet, jackup platforms are commonly employed as production structures; in water depths between about 300 and 800 feet, fixed platforms are commonly employed as production structures; and in water depths greater than about 800 feet, floating systems such as semi-submersible platforms are commonly employed as production structures.
Jackup platforms can be moved between different wells and fields, and are height adjustable. However, jackup platforms are generally limited to water depths less than about 300 feet. Fixed platforms can be used in greater water depths than jackup platforms (up to about 800 feet), but are not easily moved and typically have a fixed height. Conventional floating production systems can be used in deep water, but are relatively difficult to move between different wells. In particular, most floating production systems are designed to be moored (via multiple mooring lines) at a specific location for an extended period of time. Such mooring systems typically include mooring lines that are anchored to the sea floor with relatively large piles driven into the sea bed. Such piles are difficult to handle, transport, and install at substantial water depths. Moreover, most floating productions systems are relatively expensive and cost prohibitive for smaller, marginal oil and gas fields.
Accordingly, there remains a need in the art for offshore structures and systems designed for use in water depths greater than about 800 feet and that are easily moveable between different offshore locations. Such offshore productions systems would be particularly well-received if they were economically feasible for smaller, marginal oil and gas fields.